Morphine, an analgesic opiate, has high addiction liability. In general, there appears to be a high correlation between the analgesic action of an opiate, and its addiction liability. Until recently, very little was known about CNS sites involved in the analgesic action of morphine. Moreover, it is not know whether such analgesic sites are also involved in the development of dependence. Using the technique of intracerebral injection via permanently implanted fine-gauge (30-gauge) cannulae, we have been mapping the rat brain to find sites which mediate the analgesic action of morphine. So far, we have identified two sites, the posterior hypothalamus, and the periaqueductal gray in the mesencephalon, which mediate morphine analgesia, also results in an explosive hyper-reactivity to auditory and visual stimula which were previously neutral stimuli. Such paradoxical effects have never before been observed with systemic administrations of morphine. We are now studying the development of opiate tolerance and dependence at these sites.